Radiation sensitive fuse elements for use with a circuit board to provide more reliable sequential firing in the flash lamp array are already known. For example, U.S. Pat. No. 4,133,631, assigned to the assignee of the present invention, describes a circuit board configuration which includes such fuse elements being deposited at circuit locations wherein the underlying substrate has a thickness less than a substrate thickness elsewhere to produce holes in the circuit board by melting or thermal decomposition when activated by radiation being emitted from adjacent flash lamps. Said fuse elements are deposited on the underlying circuit board substrate and comprise at least 20% or more of a radiation absorbent solid particulate such as carbon black mixed with conventional liquid adhesive which hardens to a solid at ordinary temperatures. When this fuse material composition is deposited directly on the circuit pattern and allowed to harden at locations on the circuit board that have been recessed to enhance localized melting of decomposition of the underlying substrate, the fuse actuation produces a hole through the entire composite structure. Interruption of the circuit path is obtained in this manner to the activating flash lamp which can be disposed in a branch circuit along with a fuse element and thereby disrupt electrical connection to the already fired flash lamp.
Another type known radiation sensitive fuse element construction for use in the same general manner is described in U.S. Pat. No. 4,154,569. This type fuse element construction utilizes a strip-like element which overlies a reduced thickness area of the circuit board member and which can be constructed from a polymer film deposited on the circuit board substrate which is thereafter perforated to help isolate the absorbed thermal energy in said strip element for more reliable thermal decomposition of the entire fuse. The circuit board pattern on which said strip elements are deposited is said to be formed of metal, for example silver, nickel, tin, copper or some other readily conducting material, for example graphite. The circuit board support for the electrical circuit is also said to be pigmented in order to improve heat absorbing capacity of the overall construction and soluble dyes can also be incorporated with the thermoplastic synthetic resin composition of said dielectric support for this purpose. Additionally, a dye is recommended for incorporation in the polymer material forming a strip-like fuse element to further improve radiation absorption in the overall construction.
Still other issued U.S. Pat. No. 3,968,056 and U.S. Pat. No. 3,988,647, which are also assigned to the present assignee, describe a circuit board construction which can be used with a photoflash array wherein a particular type electrically conductive ink provides the circuit pattern. Specifically, said conductive ink comprises an organic resin matrix having sufficient particulated electrically conductive material dispersed therein to form point-by-point electrical contact when the deposited liquid ink is cured to the solid state. In a preferred embodiment, a liquid ink composition is radiation curable to provide a solid coating having electrical resistivity of less than 10 ohm-centimeters when cured. The particulated electrically conductive material providing electrical conductivity in said circuit pattern can be selected from a particulated electrically conductive metal and/or a particulated electrically conductive metal containing material which can further contain up to approximately 15% by weight of said particulated electrically conductive material in flake form with an aspect ratio of diameter to thickness greater than 20. The content of particulated electrically conductive material in said preferred embodiment is at least about 40% and not more than about 90% by weight with said particulated electrically conductive material preferably being in the form of metal coated glass spheres.